As Stuart says, IF the temp is a liquid filled type, it is sealed. Capillary tube and emersion bulb like this is NOT repairable. Throw in garbage if you don't want to test in hot water first. No voltage necessary unless you have an electric gauge/sender.
Oil pressure: Not permanently sealed, Partially undo connection at sender to see oil coming out, if so, problem is further up the line or... Undo connection at gauge to see oil pressure there (motor running) if not, Clean out tube or replace tube. If pressure there, gauge may be defective or just stuck with gunk and age. If no luck, throw in garbage and replace with aftermarket. No voltage necessary unless you have an electric gauge/sender.
I recommend replacing both with electric. Leave the gauges in dash/cluster for looks, hide electric under dash or modify new gauge face to match original look and place in cluster.
